This invention relates to turbine type of power plants and particularly to the combustor diffuser associated with an annular swirl-type burner.
As is well known, it is conventional to bleed a portion of the compressor discharge air and utilize it in the combustor for purposes other than combustion, namely, cooling and dilution. The air to the outer shroud of an annular combustor is bled off by some form of splitter and its velocity is reduced with minimum pressure losses by a suitable diffuser. As is generally well known it has been the practice to straighten the swirling flow leaving the compressor rotor by use of straightening vanes prior to its being diffused. Even in the annular swirl burner, in which a swirl component of velocity is retained at the compressor exit to enhance the mixing and combustion processes to the combustor proper, it has been necessary to straighten this swirling flow at the entrance to the outer shroud to obtain efficient diffusion in this passage. Thus, in certain installations, this portion of the combustor, that is the outer shroud, not only included the diffuser and anti-swirl vanes, but for structural reasons it also included support struts.
We have found that we can improve on the design of the splitter, diffuser and the overall annular swirl combustor to obtain a reduced combustor length with an attendant engine weight reduction and eliminating or minimizing the shaft critical speed problem as well as attaining an improvement in the assembly and manufacturing thereof. To this end the passage to the diffuser is located to take advantage of the ability of the swirling flow to negotiate a radially outward turn of approximately 45.degree. without incurring substantial losses. The support struts are canted with respect to the passage center line to receive the airflow at a predetermined incidence so as to create a quasi-pipe diffuser within the passages between struts without the need to straighten the flow. Additionally, the struts are made thicker than heretofore to provide the structural integrity, thus requiring an increased annular passage height to maintain a given flow area. Because of the increased height, radial tolerances have less influence on accuracy of the flow area. This also serves to simplify manufacturing especially if investment casting is used. By virtue of this invention in a particular embodiment, we were able to eliminate over 100 straightening vanes in the outer diameter passage, which not only simplify the assembly, manufacturing, but also resulted in a considerable cost savings.